In GSM systems, the interface between a Base Transceiver Station, BTS, and its corresponding Base Station Controller, BSC is the Abis interface. The combination of a BTS and its corresponding BSC is often referred to as a BSS, Base Station Subsystem.
Transmission of traffic over the Abis interface has evolved from TDM-based solutions to solutions based on IP, Internet Protocol. In cases where the transport network used over the Abis interface is an IP-based one, various technologies are used in order to “translate” between TDM and IP. Such “translation technologies” often increase the complexity of the GSM system.